1. Field of the Invention
The present invention concerns the field of medical engineering and relates in particular to those systems with which invasive microsurgery, invasive drug therapy, circulatory support, dilation of vascular systems, and the like, can be carried out.
In recent years, there have been enormous advances in the treatment of organs which carry fluids, particularly those of the circulatory system. The development of catheters and invasive surgery instruments makes it possible to avoid intricate operations which impose a physical burden on the patient, and to rapidly and effectively treat acute states such as sudden cardiac arrest in cases of cardiogenic shock. Common to all these methods is the fact that the microsurgery instrument used is advanced to the xe2x80x9cinsertionxe2x80x9d site through pathways which carry body fluid. Naturally, during its insertion, it greatly obstructs the flow of the body fluid there through the vessel in question, or even completely suppresses this flow.
2. Description of Related Art
Regarding the use of dilation catheters, to which the present invention is applicable inter alia, this problem has long been recognized and has prompted a number of proposals. Common to most of these proposals is that a blood flow guide system is provided inside the catheter, wherein the system has a proximal inlet and a distal outlet for blood flowing through it. These permit a passive, relatively small blood stream upon balloon dilation, brought about by the pressure difference prevailing at the dilation site (so-called autoperfusion catheter). Although the period of use of such an autoperfusion catheter is prolonged by this measure, it is still very limited because the decrease in the delivery of blood to the distally situated tissue can very quickly lead to an inadequate supply, with irreversible consequences.
An improvement was hoped for from those systems in which, with the aid of a pump, blood is actively transported through a lumen of the catheter from another vessel, for example the femoral artery (so-called active hemoperfusion catheter). However, this again has the disadvantage that a further vessel has to be tapped and the blood has to be brought to the required pressure by means of an extracorporeal, mechanical high-pressure pump and then delivered to the dilation catheter. Such a device is disclosed in the European Patent Application bearing the publication number 277 367 A1.
A further proposal envisages blood being suctioned proximally in pulses with the aid of a flap valve and of a liquid column, which can be advanced and retreated and is moved with an extracorporeal plunger, and this blood being ejected distally at the system pressure through an opening, with possible backflow being prevented by a distal ball valve. This device is already susceptible to failure because of the flap valve, it is of a complicated construction, demands the continuous supply of fresh saline solution, because the force-transmitting saline solution is not sealed off from the blood flow guide system, and can only be used in those cases where the catheter can be introduced into the relevant vessel in the direction of flow. A further disadvantage is the noncontinuous blood transport through the area of the stenosis. Such a device is shown in the European Patent Application bearing the publication number 353 889 A1.
A further attempted solution concerns the field of heart catheters. Here, it has been proposed to support a patient""s circulatory system with the aid of an intra-ventricularly expanding auxiliary pump for supporting the heart. In this pump, an outer chamber with a double wall structure can be pressurized in such a way that it expands within the ventricle, in so doing becomes rigid and adapts to the ventricle wall. An inner balloon is inflated in pulses, as a result of which the diastole and systole of the heart are alternately imitated.
However, it has never been possible to achieve clinical acceptance of such a device.
The present invention is based on the object of making available a device which can be applied in all those cases in which the use of a medical instrument is necessary whose insertion into the body obstructs the flow of a body fluid. In this connection, the device is to be constructed in such a way that the use of this instrument is nonetheless possible, or is made easier, or its possible duration of use is extended. Although the insertion in blood vessels is of course the primary concern here, because invasive microsurgery, circulatory support and the like are of great importance, the invention is not however restricted to this. It is also suitable for use in lymph, bile or, if desired, liquor, for example in invasive gallbladder operations in which the transport of the bile should not be interrupted.
According to the invention, the aforementioned object is achieved by the provision of a device for actively supporting the flow of body fluids.
The design and material of the artificial flow guide system, and its additional fittings, will depend on the envisaged application. For example, it is possible to employ the materials and dimensions used in conventional dilation catheters. Designs which are particularly suitable for special applications are described in detail below.
The artificial flow guide system has an operational area in which a pump is embedded in such a way that it can transport blood from at least one inlet opening situated in the guide system to at least one outlet opening situated in the guide system. The expression xe2x80x9cembeddedxe2x80x9d is here intended to signify that between the pump and the wall of the operational area there is as little distance as possible, preferably no distance, i.e. that the pump bears against the wall with substantial or complete sealing. In this arrangement, in specific embodiments, the pump can be driven in such a way that the body fluid can be transported in both directions, so that the device can be introduced both in co-current and counter-current with the flow of fluid through the vessel.
The design of the inlet and outlet openings will in each case depend on the type of application. The design can range from small circular openings in the side wall (e.g. arranged proximally as inlet opening), a single opening at the distal end (e.g. as outlet for a dilation catheter) or, e.g., a plurality of openings on one or both sides, right through to net-like and grid-like structures in the wall of the flow guide system.
The delivery of fluid through the pump can likewise be variable. Thus, the fluid to be conveyed can enter the flow guide system on the suction side of the pump and leave on the delivery side (at the distal end of the guide system, or else already further proximally). Alternatively, it can enter and leave on the delivery side.
The flow guide system itself must have such great flexibility that both its advance and also, and in particular, its function are possible within an optionally relatively strongly curved flow section of the corresponding blood vessel or of other fluid-carrying vessels. In this connection, preferably, the flow guide system is particularly flexible at least in a distal segment. In one embodiment, the flow guide system has a more rigid proximal segment and a more flexible distal segment. The proximal segment can have the same diameter as the distal segment, although it can also have a greater inner width. If the pump is arranged in this proximal area, it is better supported by the more rigid casing. In the case of the greater diameter of the proximal section, it is possible to incorporate a larger pump (with an improved pumping capacity). This is particularly of advantage when a very flexible, relatively long distal catheter segment is provided, in order, for example, to dilate those vessels which supply blood to the heart. In this case, the catheter can be advanced through the relatively large vessels to a point close to the area to be treated; in the treatment position, the very flexible distal segment of the flow guide system projects into the stenosed area and dilates this, for example with the aid of inflatable balloons, while the more rigid, larger catheter segment lies in a blood vessel area which has a greater diameter.
A flexible feed hose is connected to the flow guide system. The flexible feed hose can in this case be worked in one piece with or connected integrally to the flow guide system, although positively engaged or frictionally engaged connections or adhesive bond connections, or the like, are of course also possible.
In one embodiment of the invention, the feed hose too can have a rigid segment. It can also be more rigid overall than the flow guide system. If a relatively rigid segment such as this is present, or if a feed hose such as this is chosen which is more rigid overall than the flow guide system, in one embodiment of the invention said segment or the distal end of the feed hose is pushed over the proximal, flexible part of the flow guide system (or is connected securely thereto). In this embodiment, the proximal part of the flow guide system is therefore embedded in a more rigid segment, preferably in a sealing manner. Depending on the purpose for which the flow guide system is intended, the pump can in this case either be embedded in the area surrounded by the more rigid segment (that is to say on the proximal side) or can be arranged in the distal area. An advantage of its being embedded in the proximal area is here once again that the pump is better supported by the more rigid xe2x80x9couter skinxe2x80x9d.
The flexible feed hose as such is designed as a function of its application. It should preferably be of such a length that the distal end, with respect to the pump, still lies outside the body, at the furthest possible distance from the admission opening, during use.
An energy or force transmission line is guided through the interior of this feed hose. This line must be designed such that, when the device is in the operational state, it can transmit energy or force to the pump substantially continuously from a drive unit, which is outside the body in the operational state, unless it is the drive for a so-called ram pump or the like which is moved alternately forward and backward in the axial direction and is rotated simultaneously or nonsimultaneously, continuously or noncontinuously.
The aforementioned drive forms for the pump have several advantages. They permit the use of a large number of different pumps, so that, depending on the purpose for which the instrument is intended to be used, the appropriate pump can be chosen. It is possible in particularxe2x80x94but not exclusivelyxe2x80x94to drive pumps which permit a substantially continuous delivery of the body fluid, which ought to be preferable in most cases. If noncontinuous delivery is desired, then, according to the invention, it is possible to avoid fluid entering the pump from the lumen of a fluid drive column and thereby escaping to the body fluid if this is undesirable, and, in so doing, involuntarily increasing the volume of fluid surrounding the pump. Moreover, the use of valves in the pump area should in most cases be unnecessary. The drives according to the invention permit an extremely convenient handling of the medical instruments, since said admission line matches the curves of the flexible feed hose. The omission of an extracorporeal pump, which for its part has to be driven mechanically and causes losses of liquid column into the system, is likewise advantageous.
Those embodiments which have a substantially continuous drive are preferred since the extracorporeal drive means are very easy to handle. The expression xe2x80x9csubstantially continuousxe2x80x9d is intended to signify that the transport of energy or force is macroscopically continuous. This expression is intended to encompass system-related or technically induced minimal variations (or the use of alternating current or currents with microscopic changes of individual parameters). A preferred embodiment of this kind is also the transmission of force with the aid of a flexible mechanical shaft. Other continuous drive possibilities which may be mentioned by way of example here are: the electrical drive of micromotors, which in turn drive the pump or an electrical drive of pumps such as diaphragm pumps and the like.
In one preferred embodiment, the lumen of the artificial flow guide system which is provided for the flow of body fluid is sealed off from the flexible feed hose. This prevents backflow into the admission tubing, without having to work with valves.
A guide system is normally provided on one side of the device, which guide system is mostly referred to as a guide wire and which can be easily deformed, but should have a certain rigidity in the axial direction. If necessary, this can also be present as an independent subsystem, which is guided in a separate lumen of the catheter.
The pump itself can be chosen freely, and the choice will depend on the purpose for which it is intended. In most cases, continuously operating pumps are preferred. Here, miniaturized gear pumps or vane pumps are possible, while centrifugal pumps, hose pumps, diaphragm pumps or balloon pumps are further possibilities. A noncontinuously operating pump is the ram pump.
The dimensions of the pump are of course also dependent on the purpose of use. Thus, a heart catheter pump will probably have greater dimensions than pumps for dilation catheters for expanding very small vessels. All dimensions from several cm down to the mm range, or even lower, are conceivable here.
The above-described device is suitable for use in many types of medical systems, some of which are described in particular by way of example hereinbelow. Here, the normal terms for the corresponding devices are also used, without the device according to the invention thereby being limited to the forms of these instruments which are usual today. The above explanations are of course applicable in each case to these embodiments.